Mobile devices have become an integral part of the computing landscape. As mobile devices become more capable, they have shifted to perform tasks that have traditionally been performed by non-mobile computers. In one example, mobile devices may have the ability to stream media, display videos, or otherwise process large amounts of data over the course of a day. The increasing use of mobile devices by consumers, along with the high dynamic range of power consumption across mobile devices, may cause certain components of the mobile device to wear down, such as the battery. In some instances, certain applications of mobile devices may consume large portions of the battery powering the mobile device, resulting in a frequent need to charge the mobile device.
Recent developments in wireless charging technology enable a user to arrange one or more devices on, or near, a wireless charging station (e.g., a table surface with embedded wireless charging coils). The wireless charging station can charge the device(s) using wireless power transfer (WPT). Wireless power charging systems are based on transferring power using a magnetic field coupling between the two devices. In particular, a transmitter device, which is connected to a power source (e.g., an alternating-current (AC) electric power supply), can convert power from the power source into a time-varying electromagnetic field by a transmitter coil. A receiver device uses a receiver coil to convert the time-varying electromagnetic field back to electric power (e.g., direct current (DC) or AC) that can be consumed or stored by the receiver device. Wireless charging systems can form the magnetic field coupling between coils using loosely-coupled wireless charging coils or tightly-coupled wireless charging coils. In loosely-coupled systems, a small portion of magnetic flux of a transmitter coil flows thru a receiver coil, resulting in a notable size difference between the coils. Loosely-coupled system may not be sensitive to device alignment on a surface of the wireless charging station (also referred to as a pad) and can be used for charging multiple devices concurrently. Some loosely-coupled systems can exhibit poor efficiency, heating of the device, and may even charge other electronics inadvertently based on loose magnetic coupling. In tightly-coupled systems, a major part of the magnetic flux of the transmitter coil flows thru the receiver coil. In tightly-coupled systems, the coils need to be roughly equal in size and aligned to each other during operation. In some systems, instead of using a larger loosely-coupled coil, multiple smaller coils with tight coupling can be used to charge the device. Power is driven only to coils that are used for charging the one or more devices.